<template>
  <ul class="list">
    <li class="item" v-for="item of letters" @click="handleLetterClick" :key="item" @touchstart="handleTouchStart"
        @touchmove="handleTouchMove" @touchend="handleTouchEnd" :ref="item">
      {{item}}
    </li>
  </ul>
</template>

<script>
  export default {
    name: "CityAlphabet",
    props: {
      cities: Object
    },
    data() {
      return {
        touchStatus: false,
        startY: 0,
        timer: null
      }
    },
    updated() {
      this.startY = this.$refs['A'][0].offsetTop;
    },
    computed: {
      letters() {
        const letters = [];
        for (let i in this.cities) {
          letters.push(i)
        }
        return letters;
      }
    },
    methods: {
      handleLetterClick(e) {
        this.$emit('change', e.target.innerText);
      },
      handleTouchStart() {
        this.touchStatus = true
      },
      handleTouchMove(e) {
        if (this.touchStatus = true) {
          if (this.timer) {
            clearTimeout(this.timer)
          }
          this.timer = setTimeout(() => {
            const touchY = e.touches[0].clientY - 79;
            const index = Math.floor((touchY - this.startY) / 20);
            if (index >= 0 && index < this.letters.length)
              this.$emit('change', this.letters[index])
          }, 16)
        }
      },
      handleTouchEnd() {
        this.touchStatus = false;
      }
    }
  }
</script>

<style lang="less" scoped>
  @import "~styles/z.less";
  @import "~styles/varible.less";
  @import "~styles/mixins.less";

  .list {
    .flex;
    justify-content: center;
    flex-direction: column;
    .abs;
    right: 0;
    top: 1.58rem;
    bottom: 0;
    width: 0.4rem;
    .item {
      text-align: center;
      line-height: 0.4rem;
      color: @bgcolor;
    }
  }

</style>
